LNAs in RF receivers are used to boost the inbound signal level prior to the frequency conversion process, which is important in preventing mixer noise from dominating the overall front-end noise performance. A typical RF receiver is required to process a weak target signal with large interferers. A single large interferer saturates a LNA in a RF receiver, resulting in a minute gain of the target signal. This is called blocking and this single large interferer is called a blocker. Moreover, these interferers generate unsolicited inter-modulation components in the signal channel due to the non-linear characteristic of the LNA, and the inter-modulation components are then processed by the RF receiver with the target signal. These are examples of desensitization in that the receiver sensitivity (ability to process very weak signals) is compromised.
To ease signal desensitization aroused by inter-modulation components and a blocker, a surface acoustic wave (SAW) filter, a type of bandpass filter, is commonly adopted in a RF receiver to prevent the interferers from reaching LNA. The SAW filter is, however, an off-chip component which cannot be integrated, and fabrication cost may thus increase sharply. Therefore, to reduce the fabrication cost, a RF receiver without a SAW filter is a popular issue.